Purpose The aim of this study was to investigate the effect of nurse-led intervention programs on patients' physical health, physical activities, healthy lifestyle behaviors, and quality of life.,Design and Methods The research was conducted with a quasi-experimental design. The sample consisted of 33 individuals with severe mental illness. Data were collected with the Healthy Lifestyle Behavior Scale II, the Short Form-36 Quality-of-Life Instrument, and pedometers.,Findings The individuals in the intervention group showed a statistically significant decrease in waist circumference and increases in the physical activity and nutrition dimensions of healthy lifestyle behaviors and the physical function of quality of life. No statistically significant changes were detected in anthropometric measurements, healthy lifestyle behaviors, or quality-of-life subscales in the control group.,Practice Implications Mental health nursing and psychiatric nurses should plan and implement interventions to encourage healthy eating and physical activity for patients.